Microcracks tend to form in thin areas of a heat effected zone of cast metal parts as they are repaired by being fusion welded. These cracks are visible during fluorescent pentetrant, visual, and/or X-ray inspection. It is believed that the formation of the cracks is the result of an excessive build-up of heat during welding of the thin areas of a part. The excessive heat causes the formation of cracks during cooling of the part. In addition, it has been noted that preferential oxidation of surfaces of the hot metal part tends to occur.
In an effort to eliminate the formation of microcracks, the fusion welding process has been conducted with a solid copper back-up or chill. In addition, a flow of an inert gas was directed around the part. However even with the solid copper back-up and the inert gas shielding, the microcracks were still visible during fluorescent penetrant and/or X-ray inspection.